RE: [patch v4 20/24] btrace, gdbserver: read branch trace incrementally

["Metzger, Markus T" <markus.t.metzger@intel.com>]

> -----Original Message-----
> From: Jan Kratochvil [mailto:jan.kratochvil@redhat.com]
> Sent: Sunday, August 18, 2013 9:09 PM

Thanks for your review.


> > -VEC (btrace_block_s) *
> > -linux_read_btrace (struct btrace_target_info *tinfo,
> > +int
> > +linux_read_btrace (VEC (btrace_block_s) **btrace,
> > +		   struct btrace_target_info *tinfo,
> >  		   enum btrace_read_type type)
> >  {
> > -  return NULL;
> > +  return ENOSYS;
> 
> You return -EOVERFLOW in its real implementation while ENOSYS here, its
> sign does not match (+it is not documented).  linux_low_read_btrace checks
> for -EOVERFLOW.

The -EOVERFLOW return signals a buffer overflow which indicates that
delta trace is not available.  GDB then switches to a full read after discarding
the existing trace.

The -ENOSYS return signals that the feature is not available.  This error is
passed on to the user.



> > -    /* Read branch trace data.  */
> > -    VEC (btrace_block_s) *(*to_read_btrace) (struct btrace_target_info *,
> > -					     enum btrace_read_type);
> > +    /* Read branch trace data into DATA.  The vector is cleared before any
> > +       new data is added.
> > +       Returns 0 on success; a negative error code, otherwise.  */
> 
> "a negative errno code" (error code seems too ambiguous to me)
> 
> But target_read_btrace several lines above returns positive errno code.

That was a bug.  Fixed.


> TBH returning all these errno codes are not common in GDB, returning -1
> would make it easier but I do not insist on it.

I need to distinguish different types of errors, e.g. overflow and not supported.


Regards,
Markus.
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